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    <title>Document</title>
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<body>
    <script>
        var fn1 = () => {
            console.log('good')
        }

        let fn2 = () => {
            console.log('bad')
        }

        let fn3 = () => {
            console.log('normal')
        }

        fn1()
        fn2()
        fn3()


        let fn = (a, b) => {
            /* 
            a = [1,2,3]
            b=undefined
            */

            b = a
            console.log(a) // [1,2,3]
            console.log(b) // [1,2,3]

            a = '我改变了'
            console.log(a)
            console.log(b)

        }

        fn([1, 2, 3])

        // 形式参数和实际参数 可以有关系 也可以没有关系
        //形参只是在函数执行的一瞬间进行的实际参数的浅拷贝 完了只有没有任何关系了 复杂数据类型地址引用


    </script>
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